as separator -- why no article?

From Core Java Volume I—Fundamentals, 9th Edition by Cay S. Horstmann (2012):

The Java compiler itself is highly skilled in guessing the various meanings of the period character as separator between packages, subpackages, classes, inner classes, and methods and variables.

Here is what the thing that they're talking about in the excerpt looks like:

package com.horstmann.corejava // an example of a Java package
Employee.getSalary() // an example of a method call in Java

I asked my American friend why there was no article in front of separator and his answer was, first of all, that the sentence sounded completely fine to him and that you could put a definite article there, but you don't need to. As to why that was the case, no explanation followed.

Later on, he added that this is more like saying what the role is, not what the thing itself is. Alright, that makes total sense, but is there some sort of rule of thumb that can help you determine whether to use an article or leave it out altogether (whether we're talking about a role or not a role)? Obviously, the author could have gone with the "article" possibility (I don't see anything wrong with that), but he evidently didn't choose to go that way. There must have been something that prompted him to forgo sticking in an article. So, I'm really curious as to what was going on in his head at that moment and what exactly prompted him to make the decision that he made.

If you have anything to say about this grammar problem, please feel free to share your thoughts and ideas.

Answer

Here's the logic the way I see it.

See the sentence below:

Can you talk to the manager, or person acting as manager, about this?

The entire phrase "manager, or person acting as manager" are all talking about a single thing (something that is a manager or its equivalent). For example, this entire phrase could be the subject of a sentence.

The manager, or person acting as manager, is required to sign the visitor log.

So you only need one "the" in front of it, since there really is only one noun on a logical level. You can repeat the "the" for clarity if you like, but it's not required because the first "the" is still "in effect," so to speak.

It's similar to:

I wanted the blue book, blue notepad, and blue pen.

I wanted the blue book, notepad, and pen.

The first sentence is extra clear, though depending on the context the second sentence would usually mean the same.

---

Also, one other thing I can think of is that the writer of that sentence does not know if there will be one of or more than one of "packages, subpackages, classes, inner classes, and methods and variables." So ...

• 
  

  Saying "the separator between ..." would say that the period character could be the only character to separate these items.

  
  


• 
  

  Saying "a separator between ..." would say that the period character, in addition to other characters, could separate these items.

  
  

If there is a possibility that at times, you must use only period characters to separate these items, but at other times, you can use other characters, omitting the article lets the statement apply to the widest amount of cases.